Enhance VJ_DOC PDF Toolkit

I already have VJ_DOC live on Vercel and open-sourced on GitHub, but I now want to take it from “nice demo” to a polished, production-ready product. My first priority is feature enhancement, with a strong eye on smooth user flow. You will be working in a TypeScript stack (React on the front end, Node.js + REST API on the back end) and are expected to follow modern development practices, clean architecture, and secure file handling throughout.

Core enhancement goals
• Advanced file annotation that feels as snappy as native apps
• Seamless e-signature integration, including signature capture, placement, and audit trail
• Cloud-storage connectivity so users can pull from and save to services like Google Drive or AWS S3 without leaving VJ_DOC

In parallel, I need general polishing: tightening the UI for consistent behaviour across desktop, tablet, and mobile, fixing lingering bugs, improving performance, and introducing solid error handling/validation. The end result should be a fast, secure, and maintainable codebase ready for production deployment.

Acceptance criteria
1. All three new features work end-to-end in the live demo environment.
2. No critical or high-severity bugs remain in existing functionality.
3. Page-load Core Web Vitals stay in the “Good” range after your changes.
4. Code passes lint, unit tests, and PR review with clear documentation of new modules.

If you’re comfortable owning both React and Node.js pieces, optimizing for performance, and sweating the user flow details, let’s make VJ_DOC the go-to online document toolkit.